This invention relates to the catalytic dimerization, codimerization and oligomerization of olefins.
It has as its object a new catalytic composition, the codimerization or result of the dissolution of at least one nickel complex that contains at least one heterocyclic carbene ligand, in the liquid mixture, of ionic type, at least one ammonium halide and/or quaternary phosphonium halide, at least one aluminum trihalide and optionally at least one alkylaluminum halide. This invention also has as its object the use of this catalytic composition in processes of dimerization, codimerization and/or oligomerization of olefins.
Some organometallic nickel complexes that contain heterocyclic carbene ligands have been described in the prior art (International Application WO-A-99/6004, U.S. Pat. No. 5,728,839 and Patent Application EP-A-0 798 041). Application WO-A-99/6004 also describes the use of these complexes for the polymerization of acrylates and the hydrocyanation of olefins. Such complexes have the advantage of being very stable. More particularly, these monocarbene or bicarbene ligands lead to nickel complexes that are thermally and chemically stable primarily with regard to oxidation.
Some of these nickel complexes, however, exhibit the drawback of being very non-soluble in standard organic solvents, which limits use thereof. International Patent Application WO-A-99/6004 describes the preparation of carbenic cationic nickel complexes that are water-soluble. The use of water, however, cannot become general in reactions whose active catalytic radical involves a metal-carbon bond, which deteriorates in quality in the presence of protons. This is the case of the dimerization or oligomerization of the olefins.
French Patent FR-B-2 611 700 describes the use of ionic liquids that are formed by aluminum halides and quaternary ammonium halides as solvents of organometallic nickel complexes for the catalysis of dimerization of olefins. The use of such immiscible media with the aliphatic hydrocarbons, in particular with the products that are obtained from the dimerization of olefins, makes possible a better use of homogeneous catalysts. French Patent FR-B-2 659 871 describes a liquid ionic composition that results from bringing into contact at least one quaternary ammonium halide and/or quaternary phosphonium halide with at least one alkylaluminum dihalide and optionally in addition at least one aluminum trihalide. This patent also describes the use of these media as solvents of transition metal complexes, in particular nickel complexes that do not contain a nickel-carbon bond, which are transformed into catalysts for oligomerization of olefins. Below, these media will be called xe2x80x9cmolten saltsxe2x80x9d because they are liquid at moderate temperature.
During these works, it was shown that the most active nickel catalysts are obtained in xe2x80x9cmolten saltsxe2x80x9d that consist of a molar equivalent of quaternary ammonium halide and/or quaternary phosphonium halide with an equivalent (or more) of aluminum trihalide and optionally any amount of alkylaluminum dihalide. This formulation has proven particularly advantageous because the nickel complexes that are dissolved in it have a high catalytic activity.
The neutral ligands that are described in these works and optionally associated with nickel are tertiary phosphines. The drawback of the alkylphosphine ligands is that these are expensive compounds that oxidize easily in the presence of air.
It has now been found that the nickel complexes that carry at least one monocarbene or bicarbene ligand that correspond, for example, to formulas (I) and (II) that are provided below are soluble and stable in the xe2x80x9cmolten saltsxe2x80x9d media and that they make it possible to catalyze the dimerization, codimerization or oligomerization of olefins. These carbene ligands were the object of a survey in Angew. Chem. Int. Ed. Engl. 1997, 36, 2162. These are "sgr"-donor ligands and xcfx80-acceptor ligands that form very stable bonds with the transition metals. Their electronic properties can be compared to those of basic trialkylphosphines. 
The invention therefore has as its object a catalytic composition that results from the dissolution of a nickel compound that contains at least one heterocyclic mono- or bicarbene ligand in a xe2x80x9cmolten saltxe2x80x9d medium that consists of at least one quaternary ammonium halide and/or at least one quaternary phosphonium halide (Product A), at least one aluminum halide (Product B), and optionally at least one organic aluminum compound (Product C).
The nickel compounds that are used according to the invention are salts of nickel or organometallic compounds that may or may not be charged and that correspond to the general formula (already described in Patent Application EP-A-0 798 041):
(NiaXbYdLc)n(A)n 
in which:
a, b, c, d and n are integers with a equal to 1, 2 or 3; b equal to 0 to 2 times a; d equal to 0 to 2 times a; c is at least 1; n equal to 0, 1 or 2;
X and Y, identical or different, each represent a mono- or multidentate ligand that may or may not be charged; by way of examples, it is possible to cite halides, carboxylates (for example ethyl-2-hexanoate), acetylacetonate, sulfate, phenates, mono- and di-olefins, xcfx80-aromatic compounds, alkyl or aryl radicals, phosphines, phosphites and carbon monoxide;
L is a heterocyclic mono- or bi-carbene that corresponds to, for example, one of general formulas (I) and (II) above, in which R1, R2, R3, R4, R5 and R6, identical or different, each represent hydrogen, a hydrocarbon-containing group, aliphatic group, saturated or unsaturated group, or aromatic group, comprising 1 to 12 carbon atoms, and Q represents an aliphatic bivalent radical with 1 to 4 carbon atoms; and
A is a sparingly coordinating anion; by way of examples, it is possible to cite tetrafluoroborate anions, hexafluorophosphate anions, tetraphenylborate anions and derivatives thereof, tetrachloroaluminate anions, hexafluoroantimonate anions, trifluoroacetate anions, trifluoromethylsulfonate anions and acetate anions.
Heterocyclic carbenes L can be generated from corresponding imidazolium or bis(azolium) salts by deprotonation. The transition metal can play the role of reducing agent.
By way of nonlimiting examples of heterocyclic mono- or bicarbene ligands, the carbene ligands that are described by formulas (1), (2) and (3) that are given below will be cited. 
By way of nonlimiting examples of nickel compounds that can be used according to the invention, it is possible to cite the complexes of NiCl2, [dimethyl-1,3-imidazolylidene-2]2; NiI2, [dimethyl-1,3-imidazolylidene-2]2; xcfx80-allyl nickel chloride (dimethyl-1,3-imidazolylidene-2); NiCl2, [dimethyl-1,1xe2x80x2-imidazole-diylidene-2,2xe2x80x2-methylene-3,3xe2x80x2]2; NiCl2, [dimethyl-1,1xe2x80x2-imidazole-diylidene-2,2xe2x80x2-ethylene-3,3xe2x80x2]2; NiI2 [dimethyl-1,1xe2x80x2-imidazole-diylidene-2,2xe2x80x2-methylene-3,3xe2x80x2]2 and NiI2 [dimethyl-1,1xe2x80x2-imidazole-diylidene-2,2xe2x80x2-methylene-3,3xe2x80x2]2.
The xe2x80x9cmolten saltsxe2x80x9d that are employed according to the invention consist of:
a) at least one halide, more particularly a chloride and/or a bromide, quaternary ammonium and/or quaternary phosphonium (A);
b) at least aluminum trichloride and/or aluminum tribromide (B); and
c) optionally an organic aluminum compound (C).
The quaternary ammonium and/or phosphonium halides that can be used within the scope of the invention (Product A) preferably correspond to
one of general formulas NR1R2R3R4X (with the exception of NH4X), PR1R2R3R4X, R1R2Nxe2x80x94CR3R4X or R1R2 P=CR3R4X, in which X represents Cl or Br and R1, R2, R3 and R4, identical or different, each represent hydrogen or a hydrocarbyl radical with 1 to 12 carbon atoms, for example alkyl groups, saturated or unsaturated groups, cycloalkyl or aromatic groups, aryl or aralkyl groups comprising 1 to 12 carbon atoms, whereby it is understood that preferably a single one of substituents R1, R2, R3 and R4 represents hydrogen;
or else one of general formulas: 
xe2x80x83in which the nitrogen-containing heterocycles or phosphorus-containing heterocycles that comprise 1, 2 or 3 nitrogen atoms and/or phosphorus atoms consist of 4 to 10 atoms, and X, R1 and R2 are defined as above.
By way of examples, it is possible to cite tetrabutylphosphonium chloride, N-butylpyridinium chloride, ethylpyridinium bromide, butyl-3 methyl-1 imidazolium chloride, diethylpyrazolium chloride, pyridinium chlorohydrate, trimethylphenylammonium chloride and ethyl-3 methyl-1 imidazolium chloride. These salts can be used alone or in mixtures.
The aluminum halides that are used as Product B in the composition of xe2x80x9cmolten saltsxe2x80x9d according to the invention are essentially aluminum chloride and aluminum bromide.
The organic compounds of the aluminum that are used optionally as Products C in the composition of xe2x80x9cmolten saltsxe2x80x9d according to the invention have as a general formula AlRxX3xe2x88x92x, in which R is a hydrocarbon-containing radical, for example, alkyl, linear or branched, comprising 2 to 8 carbon atoms, whereby X is chlorine or bromine and x has a value that is equal to 1, 2 or 3.
By way of examples, it is possible to use isobutylaluminum sesquichloride, ethylaluminum sesquichloride, dichloroisobutylaluminum, dichloroethylaluminum or chlorodiethylaluminum.
The components of xe2x80x9cmolten saltsxe2x80x9d as defined above are in general used in molar ratios A:B of 1:0.5 to 1:3, preferably 1:1 to 1:2; Product C is used in a molar ratio with Product B that is at most equal to 100:1 and preferably 0.005:1 to 10:1. It is still necessary that the components and their ratios be such that the mixture is liquid at the temperature at which the nickel compound is introduced although the catalytic reaction of dimerization, codimerization or oligomerization can be carried out at a temperature that is less than or greater than the melting point of the catalytic composition.
The compounds that are part of the composition according to the invention can be mixed in any order. The mixture can be made by simply bringing the components into contact, followed by stirring until a homogeneous liquid is formed.
The olefins that can be dimerized, codimerized or oligomerized by the catalytic compositions according to the invention are ethylene, propylene, n-butenes and n-pentenes, alone or in a mixture, pure or diluted by one or more alkane(s), such as are found in xe2x80x9cfractionsxe2x80x9d that are obtained from petroleum refining processes, such as catalytic cracking or steam-cracking.
The catalytic reaction of dimerization, codimerization or oligomerization of olefins can be conducted in a closed system, in a semi-open system or continuously with one or more reaction stages. A vigorous stirring should ensure good contact between the reagent or reagents and the catalytic mixture. The reaction temperature can be xe2x88x9240 to +70xc2x0 C., preferably xe2x88x9220 to +50xc2x0 C. It is possible to operate above or below the melting point of the medium, whereby the dispersed solid state does not keep the reaction from proceeding smoothly. The heat that is produced by the reaction can be eliminated by all of the means that are known to one skilled in the art. The pressure can be between the atmospheric pressure and 200 atmospheres (about 20 MPa), preferably between atmospheric pressure and 50 atmospheres (about 5 MPa). The products of the reaction and the reagent or reagents that have not reacted are separated from the catalytic system by simple decanting, then are fractionated.
The following examples illustrate the invention without limiting its scope.